1. Field of Invention
The present invention relates generally to discharge manifolds and more particularly to manifolds for electrostatic gas-dynamic static discharge systems.
2. Description of the Prior Art
The problems of electrostatic, or triboelectric and atmospheric charging of an aircraft during flight is well known. The charge may be built-up by the friction of the air along the body of the aircraft, or by the blades of a propeller-driven aircraft, or by the rotors of a helicopter during flight. This charging process, together with inductive charging due to large scale atmospheric magnetic and electrical fields, has caused a problem of long standing.
As in the case of electrostatic charges, the low capacitance of the aircraft with respect to ground and the very effective insulation of the air between the aircraft and ground make extremely high potential gradients possible and result in electrostatic charges of extremely high voltages.
Generally, these built-up electrostatic charges are discharged as the wheels of the descending aircraft touch the ground and, in the case of an aircraft coming into an open runway, present no serious hazard. However, in the case of helicopters, hovering very close to ground, and dropping down cargo-hook cables, during loading and unloading, there is a very real danger of severe bodily injury if personnel come in contact with the helicopter or its cargo hooks. Even if there is no direct contact, there is still a danger of arc-over if the cable is brought too close to ground.
An electrostatic gas dynamic discharge system has been developed to meet this problem. It operates generally as shown in FIG. 1. A liquid is broken down into a minute particle vapor (analogous to the fine spray from an atomizer). These minute particles are then added to a high velocity air-stream. This particle impregnated air-stream is conducted through the channel 10 and deflected so that it flows over a high voltage electrode 12 which is connected through a power supply to the aircraft fuselage. The constricted ring 13 is a ring electrode set at ground potential. The high voltage electrode 12 in combination with the ring electrode 13 set up a high electric field region wherein ionic charges are injected into the airstream. The seed vapor flowing through this high field region condenses around these injected charges, forming charged particles with diameters ranging up to 1 micron. These charged liquid particles are carried along in the airflow of the high velocity airstream through a discharge opening out away from the helicopter.
It is important that the flow from the discharge manifold outlets be symmetrical in order to prevent electrostatic breakdown at low voltage. Such a breakdown could occur at an outlet if the air flow to that outlet was less than the flow to the other outlets. This is because the particle impregnated air flowing through the high field region draws a current therefrom thus lowering the charge build-up in the region. As the velocity of the air flow increases, the current that can be drawn increases, and thus the voltage that can be applied without arcing increases. But, if the air flow for one outlet is decreased without an attendant decrease in the voltage applied to its electrode, then electrostatic breakdown occurs.
The prior art design of the discharge manifold is shown in FIG. 2. In order to obtain the symmetrical flow to the manifolds 14, two air hoses with a "Y" connection 16 must be utilized. The rectangular shape of the manifold block 18 causes a high drag pressure on the aircraft.